Coevolution of Cryptosporidium tyzzeri and the house mouse (Mus musculus)

Abstract

Two house mouse subspecies occur in Europe, eastern and northern Mus musculus musculus (Mmm) and western and southern Mus musculus domesticus (Mmd). A secondary hybrid zone occurs where their ranges meet, running from Scandinavia to the Black Sea. In this paper, we tested a hypothesis that the apicomplexan protozoan species Cryptosporidium tyzzeri has coevolved with the house mouse. More specifically, we assessed to what extent the evolution of this parasite mirrors divergence of the two subspecies. In order to test this hypothesis, we analysed sequence variation at five genes (ssrRNA, Cryptosporidium oocyst wall protein (COWP), thrombospondin-related adhesive protein of Cryptosporidium 1 (TRAP-C1), actin and gp60) in C. tyzzeri isolates from Mmd and Mmm sampled along a transect across the hybrid zone from the Czech Republic to Germany. Mmd samples were supplemented with mice from New Zealand. We found two distinct isolates of C. tyzzeri, each occurring exclusively in one of the mouse subspecies (C. tyzzeri-Mmm and C. tyzzeri-Mmd). In addition to genetic differentiation, oocysts of the C. tyzzeri-Mmd subtype (mean: 4.24×3.69μm) were significantly smaller than oocysts of C. tyzzeri-Mmm (mean: 4.49×3.90 μm). Mmm and Mmd were susceptible to experimental infection with both C. tyzzeri subtypes; however, the subtypes were not infective for the rodent species Meriones unguiculatus, Mastomys coucha, Apodemus flavicollis or Cavia porcellus. Overall, our results support the hypothesis that C. tyzzeri is coevolving with Mmm and Mmd.

Keywords: Coevolution; Cryptosporidium tyzzeri; House mouse; Hybrid zone; Mus musculus domesticus; Mus musculus musculus.

Fig. 1

Sampling localities across the study area in Germany and the Czech Republic. The position of the Mus musculus musculus/Mus musculus domesticus hybrid zone is indicated with the dotted line. Positions of each locality along an axis perpendicular to the hybrid zone course are shown (see also Table 1); these positions are expressed relative to the westernmost locality presented in Dufková et al. (2011). Sampling site abbreviations: STR, Straas; LEHS, Lehsten; HEBA, Hebanz; BRAU, Braunersgrün; HOHE, Hohenberg; NEUE, Neuenreuth; HUR, Hůrka; WOHL, Wolfsbühl; KVET, Květná; KRAU, Krásné Údolí; PRGA, Přílezy; VER, Verušičky; BUS, Buškovice; ZIST, Žihle.

Fig. 2

Neighbour-joining (NJ) trees depicting evolutionary relationships among Cryptosporidium spp. and genotypes inferred from a partial fragment of A) the Cryptosporidium oocyst wall protein 1 (COWP) gene, B) the thrombospondin related adhesive protein (TRAP-C1), and C) the actin gene. The Kimura 2-parameter (K2P) model was used in all three trees. The bootstrap support is based on 1,000 pseudoreplicates; branches with less than 50% support have been collapsed.

Fig. 3

Evolutionary relationships among Cryptosporidium spp. and genotypes inferred from a partial fragment of the gp60 gene. The neighbour-joining tree is based on the K2P model. The bootstrap consensus tree was inferred from 1,000 pseudoreplicates; only values greater than 50% are shown.

Fig. 4

Alignment of a partial gp60 protein sequence from Cryptosporidium parvum subtype IIa (CAD98656) and Cryptosporidium tyzzeri sequences from this and other studies. N-glycosylation sites predicted by the NetNGlyc 1.0 server (http://www.cbs.dtu.dk/services/NetNGlyc/) are bolded, italicized and boxed. GenBank accession numbers are presented in parentheses.

Fig. 5

Course of infection of Cryptosporidium tyzzeri CR4293 (Mmd subtype) and CR2090 (Mmm subtype) strains in A) SCID, B) BALB/c, C) STUS, D) SCHEST mice based on a) molecular and b) coprological examination. STUS, a wild-derived Mus musculus musculus strain in 24–26^th generation of brother-sister mating; SCHEST, a wild-derived Mus musculus domesticus strain in 8–10^th generation of brother-sister mating; OPG, oocyst per gram.